1. Field of the Invention
This invention relates a method for forming an ultra microparticle-structure, and more particularly the same method suitable for forming quantum well wires and quantum well dots in semiconductor-micro processing techniques.
2. Description of Related Art
Recently, semiconductor-micro processing techniques are rapidly developed and large-scale integrations (LSIs) having dimensions of 300 nm have been realized.
On the other hand, when electrons are confined within a very small area having a dimension of several ten nm in a semiconductor, the quantum nature of electron become conspicuous. Thus, taking advantage of the nature, a new functional device such as an electron interference wave element or a single electron element which operates each electron will be realized.
Moreover, if a low-dimensional quantum structure such as quantum well wires or quantum well dots is applied for an active layer of a semiconductor laser, for example, it is theoretically predicted that the characteristics of the laser are remarkably enhanced, compared with a conventional semiconductor laser.
Thus, it is strongly desired to realize nm-scale processing techniques in a field of semiconductor-micro processing technique.
For pursuing the above object, in forming semiconductor-quantum well wires or quantum well dots, for example, a method has been developed that a quantum well structure is formed through crystal growth on a wafer, which is processed in strip and rectangle by lithography and etching, and the side walls of the processed wafer are embedded by secondary crystal growth.
Similarly, in forming a low-dimensional quantum structure such as semiconductor-quantum well wires or quantum well dots, developed is such a method using a crystal-growing technique as: {circle around (1)} a method that a strip structure is formed by using a step flow mode to grow a crystal in a transverse direction from an atomic face-step in slightly slipped surface (slightly inclined face) to the low index face of the crystal, {circle around (2)} a method that, after a three-dimensional structure with small faces called as xe2x80x9cfacetxe2x80x9d is selectively formed in openings of a substrate partially covered with amorphous film, on a part of the three-dimensional structure is formed a quantum well wire- or a quantum well dot-structure, the upper surface of which is covered with another semiconductor crystalline film, {circle around (3)} a method that, in crystal-growing on a substrate of which surface is processed in concave-convex shape, a quantum well wire- or a quantum well dot-structure is formed on the given position of the substrate by using different crystal growth rate and is covered with another semiconductor crystalline film, {circle around (4)} a method that a quantum well dots are formed of itself using distortion between heterojunction with different lattice constant, without specific processing of crystalline underlayer.
However, the former method using the crystal processing of lithography restricts a lateral confining size and brings about defects in a re-growing boundary.
Moreover, the latter method using the crystal growth technique degrades reproducibly through a step bunching phenomena or a step ordering phenomena.
Furthermore, both of the methods can miniaturize the quantum well wires or quantum well dots only up to several ten nm-scale and can not provide the ones with ideal scale of several nm.
It is an object of the present invention to provide a method for forming an ultra microparticle-structure composed of ultra microparticles of several nm-scale.
This invention relates to a method for forming an ultra microparticle-structure composed of ultra microparticles comprising the steps of:
forming on a substrate higher wettability parts and lower wettability parts to a material to be deposited,
depositing on the substrate the material to be deposited to form particles made of the material on the substrate, and
accumulating the particles in the higher wettability parts to form the ultra microparticle-structure composed of the ultra microparticles.
FIG. 1 is a general view for explaining a method for forming an ultra microparticle-structure according to the present invention.
First of all, as shown in FIG. 1(a), for example, a film 2 made of an energically unstable material to a material to be deposited is formed on a substrate 1 to lower the wettability of the whole surface of the substrate 1 to the material to be deposited.
Next, as shown in FIG. 1(b), openings 3 are formed on the surface of the substrate 1 to form thereon higher wettability parts to the material to be deposited.
Thereafter, a target made of the material to be deposited is sputtered and particles 4 made of the material are deposited on the substrate 1 at a deposition rate of 0.01-10 nm/sec.
Just then, the surface of the substrate 1 has lower wettability parts to the particles 4 due to the film 2 formed thereon. Thus, as soon as the particles 4 are deposited on the substrate 1 (surfaces 2A of the film2), they immediately migrate on the surface (the surfaces 2A of the film2) of the substrate 1. Then, when they come at the openings 3 having higher wettability thereto, they fall into the openings to be energetically stable. Therefore, the particles 4 are accumulated in the openings 3 and, lastly, as shown in FIG. 1(d), they collide and coalesce one another to form ultra microparticles 5.
In this case, a part of the particles 4 may melt at its collision. Such a melting can make the ultra microparticles 5 substantially sphere.
The sizes of the ultra microparticles 5 formed as above-mentioned are determined within the sizes of the openings 3 having higher wettabilities to the material to be deposited. Moreover, they can be freely controlled within the sizes of the openings 3 by adjusting an amount of the particles 4 to be deposited and changing the migration degree of the particles 4.
Therefore, the ultra microparticle-structure composed of ultra microparticles of several nm-scale is easily formed, which is an object of the present invention.
FIGS. 2 to 4 are TEM photographs showing an ultra microparticle-structure formed by the forming method of an ultra microparticle-structure according to the present invention.
FIGS. 2 to 4 show ultra microparticle-structures in which particles made of Au are deposited onto a substrate made of amorphous SiO2, respectively.
FIGS. 2(a) and (b) show ultra microparticle-structures formed on a substrate kept at room temperature, and FIGS. 3 and 4 show ultra microparticle-structures formed on a substrate kept at 500xc2x0 C.
FIGS. 2(a) and (b) show ultra microparticle-structures formed by depositing the particles for 20 seconds and 60 seconds, respectively. Moreover, FIG. 4 shows an ultra microparticle-structure formed by embedding openings with the same amorphous SiO2 as material composing the substrate after depositing the particles as shown in FIG. 3.
Since these TEM photographs are taken at 400,000 times, from measuring the each size of the particles in the photographs, it has a size of about 2-4 nm, respectively which is very fine. That is, the ultra microparticle-structure formed by the forming method of an ultra microparticle-structure of the present invention has ultra microparticles of nm-scale.
Thus, since the ultra microparticle-structure has particles with ideal sizes for the quantum well wires and the quantum well dots, it is expected for realizing ones with nm-scale.